Agricultural machines, such as harvesting combines and cotton pickers, typically have a hydraulically released and spring applied parking brake which is controlled electronically. In a normal operating mode, when the engine is running and the machine is moving, conventional brake circuits typically disengage the park brake by continuously energizing a park brake solenoid, which is controlled electronically by an ignition key switch located in the cab. When the key switch is in the on position, power is supplied to the park brake solenoid which keeps the park brake released. When the key switch is in the off position, the park brake solenoid is de-energized which sets the park brake.
In a towing situation, when the engine is inoperable, power must be supplied to the park brake solenoid to release the park brake. This is typically done by turning the ignition key switch to the on position which energizes the park brake solenoid. However, after the machine is towed, it is very common for an operator to believe that all of the functions of the machine are off since the engine is inoperable. As a result, the operator may forget to turn the key switch off. If this happens, the solenoid will continue to be energized and will eventually drain all of the power from the battery.
Another disadvantage of conventional brake circuits is that the key switch can be turned off while the machine is moving without turning off the engine, which is usually turned off by a push-pull cable from a throttle lever. As a result, if the machine is traveling at a high rate of speed on a road or highway and the key switch is inadvertently turned off, the park brake solenoid will be de-energized and the park brake will be engaged creating an undesirable situation.
Accordingly, it would be desirable to have a towing and brake circuit that overcomes the disadvantages described above, and to provide a simple and cost effective towing and brake circuit.